Many conventional solid state laser systems employ optical pumping means to excite solid state gain media into a lasing state. For example, in one type of conventional solid state laser system, the gain medium is a cylindrical rod, and the optical pumping means comprises elongated flash lamps positioned parallel to the rod. Radiation for optically pumping the rod is focused from the lamps onto the rod's central longitudinal axis. The rod and the adjacent flash lamps are mounted within a reflective housing. The entire assembly (comprising rod, flash lamps, and housing) is referred to as a "laser head."
Most solid state gain media in common use can be maintained at a relatively high temperature during lasing operation. However, some solid state gain media, such as Holmium:YAG material, Holmium:YLF material, and other Holmium-doped gain media, are preferably maintained at a low temperature during lasing operation (for example, a low temperature in the range from about +10 degrees Celsius to as low as about -15 degrees Celsius). A cooling system is required for this purpose, since the flash lamps (or other optical pumping means) will otherwise increase the temperature of the entire laser head (including the gain medium) to undesirably high levels.
In cases where gain medium cooling is needed, the cooling is conventionally accomplished by flooding the interior of the laser head's reflective housing with flowing coolant fluid. The gain medium and the flash lamps are thus immersed in a common volume of coolant fluid during lasing operation.
The inventor has recognized that this conventional cooling technique has several serious limitations and disadvantages. First, the conventional technique is inefficient because the heat loads due to the optical pumping means and the gain medium are generally different, and the optimal operating temperature ranges of the optical pumping means and the gain medium are generally different. If the heat load from the gain medium is substantially greater than from the optical pumping means (for example, if a lasing rod must be maintained at very low temperature, such as -15 degrees Celsius, while flash lamps need only be cooled slightly) it would be sufficient to expose the optical pumping means to a turbulent flow of coolant having much lower flow rate than the flow of coolant employed to cool the gain medium. However, the flow rate of coolant which floods the entire prior art laser head (including rod and flash lamps) is much higher than would be adequate if coolant flow were confined to regions immediately adjacent the flash lamps and a region immediately adjacent the rod, with independently controlled (optimal) flow rates in these regions.
Second, the prior art technique does not permit precise control of the gain medium temperature during lasing operation. With better control of the gain medium's operating temperature than is possible using the prior art technique, improved solid state laser performance could be achieved.